US health officials expect more cases of the coronavirus disease, Covid-19, in the coming days and weeks, even though the risk to the general public remains low.

So how will we know where those cases are and how fast the virus is spreading through the population?

The answer is simple: We need diagnostic test kits. A lot of them. And with cases of the disease confirmed in nearly 50 countries, we also need testing that focuses far beyond people with links to China, where the outbreak originated.

The problem is that testing in the US has been limited so far, with only a small number of labs available to assess the results, flaws in the manufacturing of the earliest kits sent out to states, and out-of-date criteria for testing people. (Until Friday, most tests focused on people who’d been to China recently or those with known Covid-19 exposure.)

“This has not gone as smoothly as we would have liked,” Nancy Messonnier, director of the Centers for Disease Control and Prevention’s National Center for Immunization and Respiratory Diseases, said of the testing snafus in a Friday press briefing.

The need for change became more urgent this week, when the CDC announced the first coronavirus case in a patient in Northern California with no history of travel to the countries affected and no known exposure to others with the virus. (As of Friday, the total number of cases in the US was 15. This figure does not include the 44 repatriated US citizens who were aboard the Diamond Princess cruise ship.) According to a statement from UC Davis Health, where the California patient was diagnosed, “a test was not immediately administered” because the individual “did not fit the existing CDC criteria for COVID-19.”

This means Covid-19 could already be spreading more broadly in the US than we know. Without better and broader diagnostic testing, people may be at risk. Here’s what we know about the state of the diagnostic testing in the US and around the world, and why it’s essential that these shortages are soon fixed.

There have been problems with the CDC’s Covid-19 test kits

The CDC started sending out test kits to laboratories the first week of February, a month after China announced the outbreak. But the healthy agency quickly encountered a problem.

Some labs reported to the CDC that some of the test kits were delivering inconclusive results during verification. It’s believed that one of the chemicals used to conduct the test was not working properly and needed to be remanufactured.

The tests are conducted via mouth or throat swabs, through the testing of either mucus that has been coughed up or fluid from a patient’s trachea. They’re designed to identify the virus’s specific genetic signature, and results currently have to be shipped to labs where they take a day to process.

“I am frustrated — like I know many of you are — that we have had issues with our test,” the CDC’s Messonnier told reporters earlier this week, adding that the CDC is working on modifying the kits and sending out new ones.

The problem, though, did not affect all of the test kits the CDC sent out. The Illinois Department of Public Health, for instance, reports the test kits it received are working. As of Friday, the CDC reported, the issue with the test kit ingredient has been fixed.“Right now, labs can start testing with the existing CDC test kits,” Messonnier said Friday.

So testing can and is being done in the United States. It’s just off to a slow start — even by global standards.

Not only were the test kits flawed, but few people qualified for Covid-19 testing

A few other factors stymied the ability of US hospitals to test for the virus.

One is the fact that originally, outside of the CDC, there were only 12 labs in five states that could process the tests. Now, as Health and Human Services Secretary Alex Azar said at a Congressional hearing on Thursday, there are 40 labs that can handle them. A total of 93 labs should be able to process the tests by next week.

Another has to do with the criteria for who is deemed eligible for testing in the first place. Not everyone who presents with Covid-19-like symptoms is being tested.The most common early symptoms are fever and a dry cough.

Originally, the CDC’s test criteria included only people who have traveled to China or who have been in close contact with someone known to have Covid-19.

On Thursday, the agency updated the criteria, calling for the testing of people who have traveled to impacted areas, as well as those with severe symptoms (like pneumonia) who do not have a known source of exposure and aren’t ill with another disease (like the flu). “Our criteria also allows for clinical discretion,” Messonnier said. “There’s no substitute for the astute clinician on the front lines of patient care.”

On February 14, the agency also announced it would start testing for the virus in people who hadn’t returned from China across five US cities — New York, Chicago, Los Angeles, San Francisco, and Seattle. But “that effort has not yet begun,” ProPublica reported, due to the lack of reliable tests.

“We expect the first sites to be doing testing by next week, and [we] hope to be able to rapidly move from six to all 50 states,” Messonnier said.

Meanwhile, New York, at least, has started to make its own coronavirus test kits in the wake of the CDC production errors.

The problem of slow diagnostic testing is not limited to the United States. Testing has been falling short the world over.

Until early February, only two countries in Africa — Senegal and South Africa — had the lab capacity to screen for the disease. While China has had more capacity than the US, with the ability to distribute as many as 1.65 million tests per week, according to the World Health Organization, that’s still been “entirely insufficient,” Lawrence Gostin, director of the O’Neill Institute for National and Global Health Law at Georgetown University, told Vox. “Lack of testing kits has angered doctors and patients in China,” he added, leading them to lean on things like CT scans and lung X-rays to diagnose patients.

Test shipments are still ongoing through WHO regional offices and global hubs. WHO says it will make 250,000 tests available to 159 laboratories across all WHO regions.

As of February 17, the agency had sent 3,500 testing kits to 34 countries and three regional WHO offices. As it currently stands, there are still many countries with little or no testing capacity.

Testing shortages put people at risk

There have been a couple of startling examples that show what this limit on testing means for public health — and for controlling the outbreak.

First, some people who have the virus may put others at risk while they’re waiting around to get tested. This just happened in the US. According to reports in Enterprise and the New York Times, doctors at the University of California, Davis Medical Center suspected Covid-19 disease in a patient who began seeking medical care last Wednesday.

But the patient was only tested for the virus on Sunday because the patient didn’t fit the narrow testing criteria set out by the CDC. It’s not yet clear whether this case has spawned others but it’s a reminder that limiting diagnostics can lead to (preventable) spread of the virus and also expose healthcare workers to unnecessary risk, said Peter Hotez, the founding dean of the Baylor College of Medicine. “It’s really hard for frontline healthcare workers to manage this problem,” he said.

Once one person with the disease is identified, they can be treated in isolation to not spread the disease further. Their contacts and family can be notified, and place themselves under quarantine, as to not spread the virus in the case they are already infected, but not yet showing symptoms. But without adequate testing, that’s not happening.

Just over a week ago, authorities there insisted they had no Covid-19 cases within their borders. As of Friday, Iran’s case toll had exploded to 270 — and the country now has the second highest number of deaths outside of China (26) with cases exported as far and wide as Canada and Lebanon. What this suggests, the WHO said Thursday, is that there are probably many more cases in Iran that have not been detected. And that’s already something disease modelers have predicted. In a yet-to-be-published study, researchers found there are likely more than 18,000 cases within Iran’s borders.

We need a point-of-care diagnostic test

Until we have better, faster diagnostics, doctors are still relying on a person’s travel history and assessing people’s symptoms to decide whether to test for the virus.

But with the disease now spreading in nearly 50 countries, travel history is increasingly becoming irrelevant. And symptoms aren’t always the best guide either.

Covid-19 can look a lot like other respiratory illnesses — such as flu, and the common cold. And though it’s a respiratory infection, a recent JAMA article found patients can present with abdominal symptoms, such as discomfort first. This means “we may not be detecting cases that do not present in the classic way with fever and respiratory symptoms,” said William Schaffner, an infectious disease expert at Vanderbilt University. Indeed: in the JAMA study, the patient with abdominal symptoms is thought to have infected more than 10 health care workers.

The best way to get around these risks is a point of care diagnostic test, where health professionals can — on the spot — diagnose patients with the disease. Right now, that’s far from what’s happening in the US, with specimens being sent to CDC for testing in many cases.

“The biggest worry right now in the US [is] we don’t have a point of care diagnostic,” Hotez said. “[Healthcare workers] are not going to know what they are dealing with and how to isolate patients.”

The WHO has called the development of point of care diagnostics a research priority. And when these tests are developed, they need to come at a reasonable cost.

In the US, there’s always the risk of people not getting tested due to fear of medical bills. The Miami Herald reports on a man who had traveled to China, and developed flu-like symptoms after returning from the trip. He was charged $3,270 for the diagnostic tests performed at the hospital (it turned out he had the flu). It’s easy to envision a scenario where many sick people avoid getting tested for Covid-19 because they fear what the bill could look like.

“The race is on for [rapid] testing capacity,” Gostin said. “Without it we are flying in the dark.”